70 CHEMICAL ACTION. 



Q. Why will CONTRACTING the chimney-place 



PBEVENT itS SMOKING ? 



A. As the air will then pass nearer 

 the fire, it will be more heated, and fly 

 up the chimney much faster. 



Q. Why do almost all CHIMNEYS SMOKE 

 in GUSTY weather ? 



A. The gust (blowing the air away 

 from the top of the chimney) removes 

 (for a time) all resistance to the smoke : 

 but when the wind lulls again, the 

 resistance of the air suddenly returns 

 the draught is checJced and a puff of 

 smoke rushes into the room. 



Q. What is the use of a CHIMNEY-POT? 



A. When the opening of a chimney is 

 large, the top must be contracted by a 

 chimney-pot, in order to increase the 

 draught. 



Q. How does a CHIMNEY-POT INCREASE 

 the DRAUGHT of a chimney ? 



A. As the same quantity of hot air 

 has to escape through a much smaller 

 opening, it must pass through more 

 quickly. 



Q. Why do tin BLOWERS help to get afire up ? 



